James Cameron and Sigourney Weaver on the set of Avatar. (Photo: Mark Fellman/20th Century Fox/Courtesy Everett Collection)

Pro tip: If you’re going to work with James Cameron, you’d better be prepared to get wet. Both onscreen and off, the filmmaker has long been fascinated by exploring the ocean depths, whether he’s recreating the sinking of the Titanic or exploring the Mariana Trench in his own submersible. The actors he employs frequently have to take prolonged dips as well … whether they like it or not. For Titanic, Kate Winslet and Leonardo DiCaprio memorably risked hypothermia while shooting the watery climax in freezing temperatures. And the entire ensemble of Cameron’s 1989 film The Abyss, including Ed Harris and Mary Elizabeth Mastrantonio, took a week-long course in underwater diving to prepare for what proved to be a protracted and strenuous shoot.

Now it’s the Avatar 2 cast’s turn to get hooked on Cameron’s longtime passion. Speaking with Yahoo Entertainment recently, Sigourney Weaver — who will return to Pandora in the top-secret sequel to the 2009 hit, albeit as a different character — reveals that her preproduction training included a crash course in freediving. “At least on land, I’m up to four minutes holding my breath, ” the actress boasted. “And I’m now scuba certified as well as in the midst of becoming an accomplished free diver. Once I completed my scuba course, Jim said to me, ‘The 75 percent of the world that’s underwater is now part of what your world gets to be.'”

In a separate conversation, Cameron confirmed early reports that Pandora’s ocean environments will play a major role in an ambitious slate of films that will include four installments to be released between 2020 and 2025, with an estimated $1 billion price tag. And, in fact, official casting announcements for the sequels now being shot make mention of the planet’s water-based Na’vi tribe, the Metkayina Clan. “The thing you have to remember is that we’re not doing underwater photography; we’re doing underwater performance capture,” Cameron says, adding that they’re already shooting underwater sequences in a small tank, with plans to graduate to a bigger one in January. “Nobody’s ever done that before. Just like when I was making The Abyss and Titanic, I’m way out there in the wilderness doing new stuff,” he said. “I’d be totally lost if I hadn’t done those two films and had a good sense of what works and what doesn’t work. All of that previous work was the foundation for doing the Avatar sequels.”

Weaver in her Na’vi form in Avatar. The actress will reportedly play a different character in the sequels. (Photo: 20th Century Fox/Courtesy Everett Collection)

Weaver, who first worked with Cameron in the 1986 classic Aliens, praised the director’s “ambitious vision” for the underwater performances audiences will see in the next set of Avatar films. “We’re going to have to do long takes underwater, and we won’t be wearing scuba gear because we’ll just be our characters, swimming,” she said. “There’s a whole discipline for how you build up to spending that amount of time underwater. It’s really the most fun I’ve had in a long time. I just wish the movies were coming out sooner, because I feel like the world needs more Avatar as soon as possible.”